1. Field of the Invention
This invention relates to the drying of water-wet solid materials.
2. Description of the Prior Art
Conventional methods of drying water-wet solid materials with hot air consume large amounts of energy because of the high specific heat and latent heat of vaporization of water and the poor heat transfer properties of air. Moreover, in hot air drying special measures must be taken to prevent oxidation of the material being dried. The use of gases other than air, including superheated vapors of organic compounds, for drying materials is well known. For example, U.S. Pat. No. 3,564,723 discloses the use of recycled superheated vapor, particularly steam, for drying water-wet particulate matter. Moisture is removed by bleeding off a portion of the superheated vapor. Preferably, a mixture of steam and an inert gas, such as nitrogen, is employed. U.S. Pat. No. 3,658,575 discloses drying of flexible substrates, including textile yarns, wet with an aqueous emulsion of a halogenated hydrocarbon by introducing the wet substrate into a zone filled with superheated vapors of a halogenated hydrocarbon, such as 1,1,2-trichloro-1,2,2-trifluoroethane. The halogenated hydrocarbon and water are removed. U.S. Pat. No. 3,998,588 discloses drying of water-wet textile bands by contacting the band with superheated vapor of a water-immiscible liquid which may be 1,1,2-trichloro-1,2,2-trifluoroethane or trichlorofluoromethane. U.S. Pat. No. 3,962,798 discloses drying water-wet porous materials by forced flow of a displacement liquid comprising a water-immiscible, normally liquid organic solvent, for example, 1,1,2-trichloro-1,2,2-trifluoroethan, having a surface-active agent dissolved therein through the interstices of the material, optionally followed by use of superheated vapor of the water-immiscible, normally liquid organic solvent.